> On Aug 31, 2022, at 1:21 PM, Joseph Myers <jos...@codesourcery.com> wrote: > > On Wed, 31 Aug 2022, Qing Zhao via Gcc-patches wrote: > >>> "a GNU extension" suggests a particular language feature, but I think >>> you're actually referring here to a whole language version rather than an >>> individual feature. >> >> Is “not supported by GNU extension GNU89” better? > > There are no existing diagnostics referring to GNU89 at all. I don't > think "GNU extension" needs to be mentioned in that diagnostic, but I also > think that having that diagnostic at all is ill-conceived. > >>> In any case, -std=gnu89 supports flexible array members. >> >> Yes, but only [0],[1] are supported as flexible array members. The C99 >> flexible array member [] is not supported by GNU89, right? > > C99 flexible array members are fully supported in GNU89 mode. In general, > any feature from a new language version that doesn't affect code that was > valid in previous versions is likely to be accepted as an extension with > options for older language versions.
We have a previous discussion on this: (https://gcc.gnu.org/pipermail/gcc-patches/2022-July/599067.html) And looks like that the previous conclusion was wrong… please see the following: ====== > How is level 3 (thus -fstrict-flex-array) interpreted when you specify > -std=c89? How for -std=gnu89? 1. what’s the major difference between -std=c89 and -std=gnu89 on flexible array? (Checked online, cannot find a concrete answer on this). ** my understanding is: -std=c89 will not support any flexible array (neither [], [0], [1]), but -std=gnu89 will support [0] and [1], but not []. Is this correct? If my answer to the first question is correct, then: 2. When -fstrict-flex-array=n and -std=c89 present at the same time, which one has the higher priority? ** I think that -std=c89 should be honored over -fstrict-flex-array, therefore we should disable -fstrict-flex-array=n when n > 0 and issue warnings to the user. 3. how about -fstrict-flex-array=n and -std=gnu89 present at the same time? ** When -std=gnu89 present, [] is not supported. So, we need to issue an warning to disable -fstrict-flex-array=3; but level 1 and level 2 is Okay. We also need to document the above. ==== So, from my understanding from what you said so far, -std=c89 will not support any flexible array (neither [], [0], [1]), but -std=gnu89 will support ALL flexible array including [0], [1], and []. Is this understanding correct? thanks. Qing > > -- > Joseph S. Myers > jos...@codesourcery.com
